American researchers have unveiled a two-seater electric concept car that can be taken and returned just like a shopping trolley.

Off its trolley: the grab'n'go City Car

A team of researchers at the Massachusetts Institute of Technology has developed a clever concept to make public transport a lot more appealing.

Their idea? Place a row of two-seater electric vehicles that stack into each other outside railway stations and bus depots, and let commuters use them to get to and from their final destination.

Commuters grab a fully charged car from the front of the stack to complete their trip, and drive it into the back of the stack for the return trip. The car then automatically folds itself into the stack to recharge.

Drive is via "wheel robots", electric motors mounted in each wheel. This gives the City Car (above) the confidence of all-wheel-drive, as well as allowing it to drive sideways into a car park.

However, researchers stress that the City Car is not a replacement for normal cars, taxis, buses or trucks. Instead, it hinges on the concept of a "socially responsible means of urban mobility".

Meanwhile, a Massachusetts company is developing a small aeroplane that can land, fold up its wings and drive down the highway.

Terrafugia, a company founded three years ago by graduates from the Massachusetts Institute of Technology, is building a prototype of the Transition, a six-metre two-seater the company describes as a driveable light-sport aircraft. And it's focused on building something that can take to the roads as easily as it takes to the skies.

"We're not going to have a flying car, as people think of it, for a while," said Anna Dietrich, chief operating officer of the US-based company. "I would never say it's not going to happen but today the infrastructure is not there, nor is the training, nor are the avionics that would make the training unnecessary. What makes sense right now is a (road-driveable) aircraft."